As the progress of technology, we can play the movies at home by videotape, VCD or DVD. The performance of the movie is just as that in the movie theater.
In order to achieve the entertainment performance as in the movie theater, the image and the audio effect are the most important issues for a home movie system. The image must be large enough and delicate; the audio effect of the home movie system should mimic the sound-surrounding effect in a movie theater. Therefore, the recoding equipments and the high-tech audio stereos for sound-surrounding effect are quite important. The better of the recoding software and the audio stereos, the better the performance will be.
Therefore, two specifications of audio in the DVD player including Digital Theater Systems (DTS) and Dolby Digital are widespread. The Dolby Digital (AC-3) encoding specification is established by the Dolby Laboratories. The compression method of Dolby Digital involves a twelve-to-one destructive compression process. The audio file occupies a relatively small storage space and can be transmitted by a marginal bandwidth. The Dolby Digital technology will neglect over detail in audio data, which cannot be sensed by human's ear. This is contrary to the high fidelity principle, wherein the playback sound should be as genuine as recorded one.
The audio encoding technology of DTS, which is a multi-channel media system produced by the Digital Theater Systems Company, uses three-to-one destructive compression method. It has a better performance than that of DTS even thought it is sill a destructive compression method
FIG. 1 shows an audio encoding mixer of a prior art including a delayed circuit unit 10, a level measuring unit 12, a curve control unit 14, a gain control unit 16 and an audio mixer 18. It can be seen that each technology mentioned above needs a complicated mathematical process for encoding. Therefore, a powerful CPU and a digital signal processor (DSP) and a very large physical memory should be used. That is too expensive for most of us.